1. Field of the Invention
The present invention relates to a disc brake, and more particularly to a disc brake for a bicycle.
2. Description of Related Art
A conventional disc brake in accordance with the prior shown in FIGS. 6 and 7 comprises a casing (60) having a recess (61) and a chamber (601). The chamber (601) communicates with the recess (61) and has a through hole (602) in the closed end. A bushing (603) is securely received in the through hole (602). The conventional disc brake further comprises a disc (600) mounted on a wheel (not shown).
A push block (65) is securely received in the chamber (601) of the casing (60) and has a circular hole (654) defined in the center. One side the push block (65) abuts the closed end of the chamber (601) of the casing (60), and multiple elongated egg-shaped concave recesses (651) are formed in the second side around the hole (654). Each egg-shaped concave recesses (651) has a large diameter end (652) and a small diameter end (653) with the depth of the elongated egg-shaped concave recess (651) deeper at the large diameter end (652).
A rotating block (63) is received in the chamber (601) of the casing (60) with a shaft (64) extending from one end. The shaft (64) extends through the hole (654) in the push block (65) and the bushing (603) of the casing (60). The rotating block (63) has multiple concave recesses (631) that face and correspond to one of the elongated egg-shaped concave recesses (651). A steel ball (67) received between the corresponding circular recess (631) and elongated egg-shaped concave recess (651). In normal position, the steel ball (67) is received in the large diameter end (652) of the elongated egg-shaped concave recess (651) in the push block (65).
One of two brake pads (62) is attached to the free end of the rotating block (63) and the other is aligned with the first brake pad (62) and attached to the side of the recess (61) of the casing (60). A keyed lever (66) is attached to the free end of the shaft (64) and is held in place by a locking nut (660).
The shaft (64) and the rotating block (63) are moved away from the push block (65) when the lever (66) is pulled. When the lever (66) is pulled, the steel balls are moved from the large diameter end (652) of the elongated egg-shaped recess (651) to the to the small diameter end (653) thereby generating a pushing force. The force pushes the rotating block (63) to make the brake pads (62) approach and clamp the disc (600) that is mounted on a wheel in order to apply a braking force to the bicycle.
There is a certain distance from the centers of the steel balls to the center of the rotating block (63) and the push block (65). The force arm and the output moment are inversely proportional when the input moment is fixed. The active force of the disc brake is degraded, thereby reducing the effectiveness of the disc brake.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional disc brake for a bicycle.